1. Field of the Invention
The present invention relates to a fixing mechanism for a timing gear system used in a two-shaft displacement type compressor. For example, a roots type compressor, a wankel type compressor, a screw type compressor, etc.
2. Description of the Related Art
A fixing mechanism for a timing gear system is shown in Japanese Utility Model Laid-open Publication 60-143182 and Japanese Patent Laid-Open Publication 63-179192. As seen in FIGS. 6 and 7, they disclose a two-shaft displacement type compressor which has a pair of rotors 61, 62 that rotate to suck in a fluid and exhaust it.
In the mechanism of FIG. 6, the rotors 61, 62 rotate together, with a slight gap (0.2.about.0.5 mm), by the engaging of timing gears 65, 66 fixed to shafts 63, 64 by keys 67, 68. The timing gears may instead be fixed to the shaft by a spline (not shown in FIG. 6).
In the mechanism of FIG. 7, tapered faces are formed on shafts 71, 72 and on timing gears 73, 74. The timing gears 73, 74 are fitted to the shafts 71, 72 on the tapered faces and are fixed thereto by bolts 75, 76.
However, these known fixing mechanisms for a timing gear system have the following defects.
A key groove restricts a setting position of the timing gear to the shaft. Therefore machining errors and setting errors of the key grooves of the timing gear and the rotor, and in the sectional form of the teeth of the timing gear, can cause a phase difference of the rotors. In order to avoid the defect, it is necessary to maintain high cutting accuracy. But such machining is very difficult and therefore productivity falls off and manufacturing costs increase greatly. In order to avoid contact between the rotors, it is necessary to design the gap between the rotors to be large. Therefore the compression characteristics of the key-type compressor are poor.
On the other hand, in a compressor having shafts formed with a tapered face, errors in the taper angle and the diameter of the tapered face cause axial aberrations of the timing gears. Also, it is difficult to use a spacer between the step of the shaft, the bearing and the timing gear, because a gap then occurs between the tapered faces.